The angiogenic peptide vasodilator adrenomedullin (AM) signals through a G-protein coupled receptor (GPCR) called calcitonin receptor-like receptor (CLR) when the receptor is bound to a novel class of proteins called receptor activity modifying proteins (RAMPs). Using genetically engineered mouse models lacking each of the components of AM signaling, we have consistently identified a rare type of embryonic lethality that is characterized by generalized edema caused by defects in lymphangiogenesis. We hypothesize that AM signaling in endothelial cells is an essential mediator of lymphangiogenesis during embryonic development. Our long-term objective, to define the function of AM signaling during lymphatic vascular development can be met in the following aims: Specific Aim 1 is geared toward determining the cellular origin of the lymphatic vascular defects and the dosage of AM signaling required for normal lymphangiogenesis. We will generate and characterize novel genetic mouse models to elucidate i) if AM signaling in endothelial cells is necessary for normal lymphangiogenesis ii) if AM signaling in endothelial cells is sufficient to support normal lymphangiogenesis and iii) the minimum dosage of AM required for normal lymphangiogenesis. Specific Aim 2 will test the hypothesis that AM is a potent modulator of lymphatic endothelial cell proliferation and permeability due to preferential expression of its receptors in lymphatic versus blood endothelial cells. Results from this aim will distinguish genotypic and phenotypic differences between lymphatic and blood vascular cells and will provide a mechanistic basis for the underlying cause of hydrops in the null mouse models. In Specific Aim 3, we plan to identify genetic pathways that interact with the AM Signaling System to modulate its functions either in healthy or edematous lymphatic vasculature. The functional significance of positively identified pathways will be confirmed through an embryoid body culture system, in vivo corneal neovascularization assays and tail microlymphography. Results from this aim will define the functional consequences of altered AM activity in the lymphatic vasculature and will elucidate how this pathway interacts with other pathways to mediate lymphangiogenesis. By completing these aims we hope to provide novel insights into the processes that govern lymphangiogenesis during development and thus identify a new class of protein targets which can modulate the lymphatic vasculature for the treatment of conditions such as lymphedema or the inhibition of tumor metastasis. PUBLIC HEALTH RELEVANCE We have demonstrated that genes required for mediating the signal of a potent angiogenic peptide, adrenomedullin, are required for lymphangiogenesis during embryonic development. We plan to elucidate the functions of AM signaling in the lymphatic vasculature. In doing so, we hope to provide novel insights into the processes that govern lymphangiogenesis during development and thus identify a new class of protein targets which can modulate the lymphatic vasculature for the treatment of conditions such as lymphedema or the inhibition of tumor metastasis.